For anyone who remembers the surreal delights of Monty Python, the sight of a rabbit behaving like a ferocious beast, or a perfectly respectable scene descending into utter absurdity, may bring back happy memories. Terry Gilliam and the Python team understood that humour often works best when the familiar is turned on its head. But this particular brand of eccentricity has a history stretching back centuries.

During a recent visit to Florence, Raph and I discovered wonderful examples of this at the San Marco Museum, where La Biblioteca Svelata: Il Bestiario Fantastico (The Library Unveiled: The Fantastic Bestiary) explored the extraordinary creatures lurking within medieval manuscripts. The exhibition brought together illuminated books dating from the 13th to the 16th centuries, revealing a world of familiar animals, fantastic beasts and curious hybrids.

Archangel Michael slaying a Dragon c.1450 Some creatures had serious business to attend to. Dragons, for example, might appear alongside saints who had heroically defeated them, carrying a clear religious message. Elsewhere, however, these strange animals seem to escape the confines of symbolism and become exercises in sheer imaginative invention. In the marginal decorations of medieval manuscripts you may encounter rabbits with weapons, snails confronting knights and creatures that seem to have wandered out of a particularly eccentric dream.

Not every image was intended as a joke, and its original meaning is not always clear. No doubt those talented artists and calligraphers were only too aware of general illiteracy; without the images these pages would have been perceived by many simply as a series of black lines! Yet there is something wonderfully familiar about the medieval artist's delight in the unexpected. Like Monty Python’s killer rabbit Beast of Caerbannog these anonymous craftsmen understood the comic possibilities of turning the natural order upside down.